If the operating plunger is not attached to the operating member correctly, or if the operating unit is not positioned or installed correctly, or the screw connection for the operating plunger has become loose by vibration, then operation of at least one switching element by the operating unit may no longer be ensured, without this being noticeable. In this case, an emergency-off circuit will remain closed, despite operation of the emergency-off switch. The emergency-off switch will therefore lose its functionality and thus its protective function. This also applies in a corresponding manner to control units in general. This can lead to unpredictable damage to people and installation parts in control installations.
DE 103 48 884 discloses a control unit in which spatial association is monitored by way of a transponder, which is fitted to the operating member, and corresponding read unit on the appliance.
DE 203 05 818 discloses a safety element for a control unit, which is in the form of an additional part which can be lead-sealed, with the additional part which can be lead-sealed being located behind the switchgear cabinet door or in the interior of a housing, and being unsuitable for visual or mechanical checking.